1. Field of the Invention
The present invention relates to a catalyst comprising a support body and a catalytically active oxide composition of the formula IMo1VbMc1Md2On  (I),where                M1=Te and/or Sb,        M2=at least one element selected from the group consisting of Nb, Ta, W, Ti, Al, Zr, Cr, Mn, Ga, Fe, Ru, Co, Rh, Ni, Pd, Pt, Bi, B and Ce,        b=0.01 to 1,        c=0.01 to 1,        d=0.01 to 1 and        n=a number required to achieve electrical neutrality and determined by the valence and abundance of the elements other than oxygen in (I),applied to the surface of the support body.        
The present invention also relates to the use of the above-described coated catalysts as catalysts for the heterogeneously catalyzed gas-phase oxidation of propane to acrylic acid.
2. Discussion of the Background
Multimetal oxide compositions having a stoichiometry corresponding to the formula I are known (cf., for example, EP-A 608838, EP-A 529853, JP-A 7-232071, JP-A 10-57813, JP-A 2000-37623, JP-A 10-36311, Proceedings ISO'99, Rimini (Italy), Sep. 10–11, 1999, G. Centi and S. Perathoner Ed., SCI Pub. 1999, EP-A 767164, Catalysis Today 49(1999), pp. 141–153, EP-A 962253, Applied Catalysis A: General 194 to 195 (2000), pp. 479 to 485, JP-A 11/169716, EP-A 895809 and DE-A 19835247) and have also been proposed in the earlier patent applications DE-A 10029338 and DE-A 10046672. Multimetal oxide compositions having a chemical composition like that of the oxide compositions of the formula (I) are also known from WO 00/29106.
The use of multimetal oxide compositions having such a catalyst composition for the heterogeneously catalyzed gas-phase oxidation of propane to acrylic acid has already been proposed in the above-cited prior art.
Acrylic acid is an important ethylenically unsaturated compound which is used both as such and also in the form of its alkyl esters for preparing polymers.
An aspect common to all publications of the above-cited prior art is that they use the multimetal oxide compositions of the formula (I) in crushed form for the catalysis of the gas-phase oxidation of propane to acrylic acid.
Although this gives the catalyst charge an increased activity, which is advantageous in the case of the relatively unreacted propane, the significantly more valuable catalyst property, namely the selectivity of acrylic acid formation, is not fully satisfactory when crushed multimetal oxide compositions are used.
DE-A 4442346 relates to a process for producing coated catalysts comprising multimetal oxide compositions similar to those of the formula (I).
DE-A 4442346 recommends these coated catalysts as catalysts for the gas-phase catalytic oxidation of acrolein to acrylic acid.
EP-A 1090684 is also relevant prior art.